Solid state electronic devices efficiently interacting with the electromagnetic radiation of various spectral ranges are the basis of state-of-the-art communications, space and other emerging technologies. This rapidly growing market became available due to the effects of electron-hole pair generation and recombination in the semiconductor materials. The most practical material system for these optoelectronic applications is the variety of alloys comprising Group III elements (Boron, Aluminum, Gallium, Indium) and Group V elements (Nitrogen, Arsenic, Antimony) of the Periodic System. This material system provides semiconductor materials with band gaps ranging from about 80 meV to over 6 eV, thus covering spectral ranges from mid-infrared (mid-IR) to deep ultra-violet (deep UV), or the wavelength ranges from about 16 micrometers to 200 nanometers.
The two major requirements for the compound semiconductor technology are extremely low defect density and precise control over the alloy composition. This last requirement means basically that the material for this technology must be prepared artificially, using one or more of the methods of crystal growth available to the skilled artisan. The choice of the growth method directly affects the material quality; in another words, the defect density, purity and compositional uniformity.
Currently, the most conventional crystal growth method used for the compound semiconductor material is Epitaxy. In this method, the material is assembled from atoms provided by atomic sources which are then deposited at the surface of a bulk crystal, which is called the Substrate. The different types of Epitaxy are distinguished by the atomic sources types. The said sources can be liquid or gaseous by phase, and atomic to chemical compounds by composition. Accordingly, there exist Liquid Phase Epitaxy (LPE), Molecular Beam Epitaxy (MBE) and Vapor Phase Epitaxy (VPE). Among the Vapor Phase Epitaxy, the best results for the compound semiconductor growth are reported using Metal-Organic Vapor Phase Epitaxy, where the elements of the Group III are supplied by gaseous metalorganic compounds, such as trimethyl-metals, triethyl-metals, or the like. Each method has its advantages and limitations related to the particular material composition to be grown.
In each epitaxial growth method, the resultant material quality depends strongly on the substrate used. In addition to the substrate crystal quality, the important parameter affecting the result is the lattice mismatch between the substrate and the epitaxially deposited film. Large mismatch leads to the mechanical strain in the epitaxial film, which in turn is relaxed through the development of structural defects as the film thickness increases. To create a high quality bulk layer, it is necessary to reduce the lattice mismatch between the epitaxial film and the substrate for each particular film composition.
The substrate for the epitaxial film deposition must be a bulk crystal that is able to provide proper mechanical support. Bulk crystals are typically obtained by methods other than epitaxial deposition and are in most cases limited to binary compounds of the Group III and Group V elements. Thus, only discrete values for the substrate lattice constants are available for compound semiconductor epitaxial growth. Several methods were developed in the past to overcome this limitation. These methods are summarized in the Prior Art section of this disclosure.
While nearly all compound semiconductors suffer from the absence of native or lattice matched substrates, the situation is probably most critical in the narrow band gap compounds, such as antimonides or arsenic-antimonides. Gallium Antimonide GaSb, Indium Antimonide InSb and their ternary and quaternary (with addition of Arsenic) compounds have the largest lattice constant of the III-V compounds, and offer exclusively narrow band gaps of 0.08 to 0.6 eV, which corresponds to an electromagnetic radiation wavelength of 2 to 16 micrometers. This spectral range is extremely important for a variety of applications including, but not limited to, radar, communications, and space monitoring. However, for effective interaction with electromagnetic radiation of this spectral range, and especially for the effective absorption of radiation in detection and photovoltaic applications, layers of the material with thicknesses in micrometer scale (depending on the absorption coefficient) are needed. These thicknesses are well above the critical thickness for strain relaxation in the strained crystalline film, so that epitaxial growth of these compounds on the lattice mismatched substrate results in high defect density developed due to the said strain relaxation.
It is therefore desirable to develop the method of growth and fabrication of infrared photodetectors comprising III-V alloys with high Antimony compositions of high quality and appropriate thickness.